The present invention relates to ultrasonic control systems for cut-off or shearing machines. A cut-off machine is a shear that cuts steel bars into lengths called "molts" that are subsequently forged into shaped parts. The forging process requires molts of precise weight: if they are too light, they will not fill the mold, and if they are too heavy, they can break the machine. Usually, off-weight molts are scrapped because the hand processing required to make them usable costs more than does the loss as scrap. Since steel bars currently cost approximately $0.20/lb., and scrap sells for about $0.6/lb., a molt weighing up to about 20/lbs. can result in a scrap loss of about $3.00. Presently, approximately 20 to 30 percent of molts are scraped leading to scrap losses of $80,000/mo. for a cold forge of a typical commercial size. Hence, reductions in scrap losses can equate to substantial savings per machine.
The present invention is directed to solving this problem and relates to the use of ultrasonics to automate the cut-off machine to achieve more precise weights in the molts specifically by ultrasonically measuring or calipering the bar diameter as it is fed into the machine and adjusting bar stock length severed by the cut-off machine to compensate for the change in diameter from a predetermined diameter.
According to the present invention, opposing pairs of transducers are mounted to opposing sides of the path where the bar travels to ultrasonically caliper the bar stock on one diameter, and, a corresponding opposing pair is oriented transversely to the first pair to ultrasonically caliper the bar stock on another diameter so that each pair bisects a line passing through the opposing pair. A pair of the transducers is selected as the control pair and distance measurements between each transducer of that selected control pair to the surface of the bar stop is measured and all four transducers as a unit are adjusted by an adjustment motor so as to eliminate any difference in distance between the two opposing control parts. In this way, the transducers are precisely aligned with the central core axis of the bar stock and distance or caliper measurements between all four transducers then produce an accurate measure of the diameter of the bar stock in a highly expeditious and inexpensive fashion.
A speed of sound measuring transducer, as disclosed in my pending application Ser. No. 149,816 filed Jan. 29, 1988 now U.S. Pat. No. 4,938,066 and incorporated herein by reference, is utilized to provide a signal input which is a highly accurate measure of the velocity of sound in the medium which is utilized to compensate for any speed of sound variation in the air space between the bar stock and each of the transducers. One or more wheels are used to measure the movement of the bar stock and provide interrupt signals in the absence of bar stock material. The four signals from the opposing transducer pairs are utilized to compute the diameter of the bar stock and compute the length of bar stock needed to produce a given volume. In the conventional machine, a bar stock end sensor member is engaged by the leading or free end of the bar of stock and moved therewith. A rod member is moved with the end sensor member and the position of an adjustable magnet is sensed by a position sensor (similar to a proximity switch) so as to provide a signal corresponding to the end of the bar stock. Other displacement sensing devices well known in the art, such as optical discs, linear potentiometers, photo cells, etc., can be used to sense the amount or distance the end sensor moves. When the proper length of bar stock is fed into the shearing position, a grab or clamp mechanism secures the end portion being sheared while the shear is operated. In the shear machine, in the initial set-up, the operator adjusts the position of the magnet (using a calibrated dial) to thereby adjust the length of the bar stock to be sheared. The present invention augments this manual system by dynamically measuring and adjusting the sensed position of the leading end of the bar stock as a function of the change in diameter to assure that the volume of metal in the sheared sections are uniformly the same. A conventional computer terminal may be utilized to input factors such as the nominal diameter of the bar stock, the nominal length of molts desired.